When installing or implementing semiconductor devices and/or optical devices as represented by LSIs (Large Scale Integrated circuits) and LCDs (Liquid Crystal Displays), solder balls are used to produce electrical connections. In recent years, investigations have been carried out into mounting minute particles that are conductive balls including solder balls and other type of balls made of any conductive metals or balls coated with metal, with a diameter of 1 mm or less onto a substrate.
Japanese Laid-Open Patent Publication No. H09-148332 (hereinafter reference publication 1) discloses one example of a technology that arranges minute particles at desired positions. This publication discloses moving minute particles on a mask with apertures for arranging the minute particles by a moving means called a squeegee that has a predetermined softness to insert the minute particles into the apertures, with the minute particles being arranged held on a porous substrate by the suction air.
The squeegee in the reference publication 1 is used to move excess particles that have not been inserted into the apertures. In the reference publication 1, the squeegee is moved by being attached to a belt that moves in a linear direction above the mask. The reference publication 1 also states that above the mask in which a ring-shaped gutter is formed, the squeegee that is attached to a disc-shaped holding member is moved along the gutter. In either case, the minute particles are moved by the squeegee in one predetermined direction. A squeegee that moves back and forth is also disclosed, but in such case, the movement direction consists of just two directions, an “out” direction and a “return” direction.
In the reference publication 1, by inserting the minute particles into the apertures using suction air, the minute particles are appropriately arranged at the necessary positions. Regardless of the presence or absence of suction air, one condition for the minute particles, that is, the conductive balls, to fill the apertures or openings provided in a pattern in the mask without missing any apertures is for a sufficiently large number of conductive balls to be supplied relative to the number of apertures (the density of the apertures). However, if the number of conductive balls is large relative to the number of apertures, time (life time) of moving the conductive balls over the surface of the mask becomes long. During the time, due to a number of factors, such as contact with the atmosphere, contact between balls, contact between the balls and the mask, friction and contact between the balls and the squeegee, abrasion and deformation are caused for the surfaces of the balls, which reduce the performance of the balls as electrodes. Accordingly, if a large number of conductive balls are moved in an attempt to reduce the number of unfilled apertures, or to reduce arrangement errors or mounting errors for a substrate (work) due to unfilled apertures, there is an increase in the probability of problems occurring for the conductive balls disposed on the substrate. In addition, when a method that moves a large number of balls is used, since it is necessary to discard a large number of conductive balls that have not been disposed, there is an increased rate of loss for the conductive balls that is not preferable from a cost perspective.
When the conductive balls are moved in the same direction by the squeegee, due to the squeegee conditions, the mask conditions, and the like, variations in density of the conductive balls are likely to occur in the longitudinal direction of the squeegee, which can lead to fail of filling of apertures and fail of placing of balls. When the amount moved by the conductive balls is increased in an attempt to improve the yield, this results in an increased loss of balls in the same way as described above. In the apparatus described in the reference publication 1, the squeegee is moved back and forth over the mask to reduce failure of filling the apertures. However, since the number of particles inserted into the apertures during one time of the movement of the squeegee falls when the times of the back and forth movement are increased, the damage to the particles due to such movement proceeds.